Conventionally, a hydraulic actuator is used in many of transmissions. However, the hydraulic actuator is not good at responsiveness, and the characteristics are changed depending on an environmental factor such as a temperature. In addition, since a hydraulic pressure generator is necessarily mounted, the hydraulic pressure generator may become a deterioration factor such as costs, weight, and volume.
On the other hand, even though an electric mechanism component such as an electric motor has a merit on a less change in characteristics such as the responsiveness and the environmental factor, there is a problem in that a power capacity and a mechanical output are small. Therefore, even though there is an idea of technically electrifying an actuator for a transmission for quite a while, the idea has not been realized due to the above problem, and thus the most part is occupied by the hydraulic drive.
However, the above problem has been solved as a recent electrifying technology is improved. Therefore, a product made for electrifying an electric oil pump even in the transmission is commercially available.
Regarding the electrifying of the transmission, there is known a technology in which a stepping motor adjusts a hydraulic pressure of a hydraulic oil to be supplied to a primary pulley of a belt-type continuously variable transmission (for example, see PTL 1).